Electrical conductive floor tile and method for making same

ABSTRACT

This invention pertains in general to electrically conductive floor tiles and particularly to floor tiles composed mainly of thermoplastic material to which electrically conductive material, in the form of great quantities of small flakes, are formed in multiple layers so that a pattern composed of streaks of these flakes appear on the surface and bottom of the tile thereby providing a conductive floor tile with a volume resistivity in the order of 1012 to 1013 ohm-cm., with a maximum electrical charge of less than 10 12 coulomb/cm2.

United States Patent Shirai et al.

[4 1 Oct. 29, 1974 I ELECTRICAL CONDUCTIVE FLOOR TILE AND METHOD FOR MAKING SAME {76] lflVBl'ltOfSl Sakae Shirai, No. 1823 Nakanoshima, Kawasaki; Keigo Sasamoto, No. 2100 Yamazakicho, Tokyo, both of Japan [22} Filed: Oct. 26, 1971 [21] Appl. No.: 192,350

Related [1.8. Application Data [63] Continuation of Ser. No. 829,870, June 3, 1969,

abandoned.

{52] U.S.Cl 317/2 R, 161/212, 252/511, 317/2 G {51] Int. Cl. 1105f 3/00 {581 Field of Search 317/2 G; 161/162, 163, 161/212; 252/511 [56] References Cited UNITED STATES PATENTS 1,873,587 8/1932 Humphrey's ct a1 161/212 zzaazaaaraaaa, 'I'YI/I/III/l/IIIYlI/IY 2,325,414 7/1943 McChcsney et al. 317/2 G 3,035,955 5/1962 Zucker et a1. 317/2 G 3,040,210 6/1962 Charlton et a1 161/212 3,194,856 7/1965 Palmer 161/162 3,386,001 5/1968 Slosberg et al. 161/162 Primary Examiner-J. D. Miller Assistant Examiner--Harry E. Moose, Jr, Attorney, Agent, or FirmJay M. Cantor [57] ABSTRACT 6 Claims, 10 Drawing Figures PMENTEUIIBT 29 1914 3545; 353

SIIEEI 1 0F 2 ELECTRICAL CONDUCTIVE FLOOR TILE AND METHOD FOR MAKING SAME This is a continuation of application Ser. No. 829,870, filed June 3, W69, now abandoned,

The volume resistivity of known types of floor tiles within the range of l-Smm. in thickness and l50 350mm. X 150 350mm. in size is approximately in the order of 2 X l ohm-cm. and therefore the maximum electrical charge caused by the friction of pedestrians shoes can reach the order of 9 X lU coulomb/cm? Furthermore, the electrical charge fails to leak away and accumulates. For this reason. dust is attracted and not only forms dirt, but can cause sparks to fly between persons. Therefore, when used in rooms with electronic apparatus there could be disruption in the operation of the apparatus. When used in operating chambers the accumulated charge could cause an explosion by igniting anesthetic gases. To prevent accumulation of electrical charges as previously described, recent developments consist in homogeneously mixing metal powders or carbon powder with polyvinylchloride to form conductive floor covering material. However, the mixing of metal powders produces a surface from which the powder is easily dislodged and which has low resistance to wear and is liable to crack due to its brittle composition. The mixing of carbon powder produces a black color and therefore prohibits other colors or the formation of designs. Furthermore the inherent strength of the tile is reduced and the breakage factor increased.

An important object of this invention is to provide a conductive floor covering or floor tile, composed mainly ofthermoplastic material, which features: Freedom in selecting colors and designs; is chemically stable; has great mechanical strength; has volumetric resistance of less than It) l0 ohm-cm; the maximum accumulated static charge is less than coulomb/em t; the resistance remains constant with aging; and is wear resistant and can be produced at low cost.

Another object of this invention is to provide a conductive floor tile or floor covering composed mainly of thermoplastic material which features: conductive material contained therein in the form of numerous thin small flakes in multiple layers so that patterns formed by these flakes appear on the top and bottom surfaces.

Still another object of this invention is to provide a conductive floor tile or floor covering, composed mainly of colored thermoplastic material which features conductive material contained therein in the form of numerous small thin flakes in multiple layers so that patterns formed by these flakes appear on the top and bottom surface in contrast with the color of the base material.

Yet another object of this invention is to provide a conductive floor tile or floor covering, composed mainly of colored thermoplastic which contains conductive material in the form of numerous small flakes in multiple layers so that patterns formed by these flakes appear on the top and bottom surface and which features a conductive sheet covering the bottom surface.

Another object of this invention is to provide a conductive floor tile or floor covering composed mainly of colored thermoplastic material which contains conductire material in the form of numerous small flakes in LII multiple layers so that patterns formed by these flakes appear on the top and bottom surfaces, and which features a conductive sheet covering the bottom surface and a pattern formed by the flakes on the top surface which is in contrast with the color of the base material.

Yet another object of this invention is to provide a conductive floor tile or floor covering composed mainly of colored thermoplastic material which contains conductive material in the form of numerous small flakes in multiple layers, and which contains a conductive sheet sandwiched within the base material.

Still another object of this invention is to provide a conductive floor tile or floor covering composed mainly of colored thermoplastic material within which conductive material is contained in the form of numerous small flakes in multiple layers, said body containing a conductive sheet sandwiched within the base material, the flakes forming a pattern on the top surface in contrast to the color of the base material.

These and other objects ofthe invention will be manifest upon reading the following explanation in conjunction with the accompanying drawing wherein:

FIG. I is an explanatory drawing depicting the pro cess of manufacturing roughly rolled sheets.

FIG. 2 is an explanatory drawing depicting the rolling apparatus for rolling the basic rough sheets into sheets of the final product and blanking to form the tiles.

FIG. 3 is an isometric enlarged view of a block section of the floor tile.

FIG. 4 depicts the process for manufacturing a different type of tile from the basic roughly rolled sheet.

FIG. 5 is an isometric enlarged view of a block section of the different type of tile.

FIG. 6 depicts the process for manufacturing another different type of tile from the basic roughly rolled sheet.

FIG. 7 is an isometric enlarged block section of another different type of tile.

FIGS. 8 and 9 depicts the process for manufacturing still another different type of floor tile.

FIG. 10 is an isometric enlarged block section of still another different type of floor tile.

The floor tile and floor covering which is the subject matter of this invention features very beautiful color combinations provided by changing the colors of the basic material and of the conductive material which is in the form of multiple layers of numerous small flakes and which form contrasting color patterns on the surface of the tile. Furthermore the product is chemically stable, wear resistent, easy to produce and can be manufactured at low cost.

The floor tile and floor covering herein described is comprised of conductive material in the form of numerous small flakes contained within the base material in multiple layers, numerous flakes appearing on the top and bottom surfaces. A sheet of conductive material covers the bottom surface or is sandwiched within the conductive body material to form an integral laminate. The afore-described numerous conductive flakes in multiple layers make contact with each other, one above the other, or are separated by extremely small distances, therefore the charge accumulated in the surface is readily discharged to ground. The charge accumulated on the part ofthe surface which is not covered by a small flake will be concentrated towards the nearest conductive flake and therefore the charge becomes readily dissipated. The conductive sheet applied to the bottom surface or sandwiched within as a laminate, further helps to discharge the electro-static charge by readily grounding the charge accumulated on its surface.

The amount of conductive material in the form of conductive flakes or conductive sheet. which is utilized in this invention depends upon the thickness of the floor covering. on the place of usage, or on the characteristic of the conductive material. The amount represents from 5 to 50 percent of the weight. The amount of conductive material within the conductive flakes or conductive sheets represents approximately 5 to 40 percent of the total weight. The amount of conductive material is controlled so that the volume resistivity of the floor tile or floor covering is in the order of 10 to 10" ohm-cm. and the maximum surface charge below 10' coulomb/cm v The volume resistivity suitable for homes is in the order of It)" to l ohm-cm. whereas for rooms containing electronic equipment and operating chambers, resistivity of the order of 10 to l0 ohm-cm. is recommended. However the above usages are merely examples and do not restrict the application in any way.

The conductive floor tile or floor covering herein described readily discharges or grounds surface charges acquired through friction or through contact with other charged bodies. This not only prevents dirtying or soiling of the floor tile or covering which results from dust particles adhering to the surface. but provides a readily cleanable surface. Charges accumulated on persons or articles placed on the floor are also readily discharged and thereby prevent shock hazards, static interference in electronic equipment. and explosive hazards caused by the igniting of inflamable gases by electro-static sparks in operating chambers.

The ratio ofthe ingredients contained in the thermoplastic body material. and of the coloring flakes contained in ordinary floor tiles and coverings vary considerably. The following table gives the ratio in weight of ingredients in a representative polyvinylchloride tile with ideal ratios given in columns (A) and (B).

A 8 Pulp inyl Chloride I00 I00 I00 PI;|. llLl/Lf Ill-70 45 35 Stabili/er 3-20 Ill (1 Pigment I50 I l Calcium Carbonate ll- 50 150 ll Asbestos ll--:llll lllll (I The coloring flakes are prepared from mixes A or B by rol|-mixing the ingredients and forming sheets of 3 C D Pnl \\|n \l hlornle lllll Illll lllll Pl.t\llt.tlt.l Ill-Hill bl) 5t Stabilizer J 4 -Continued C D Carbon Powder 20-300 I50 50 Calcium Carbonate 0-300 50 0 Asbestos 0-200 l0l) 0 The conductive flakes are prepared from mixes C or D by roll-mixing the ingredients and rolling into sheets of 3 to 6mm. thickness whereafter the sheets are cut into slugs of suitable size within the approximate range of 2 to 5mm X 2 to 5mm. After cutting. the slugs are hardened and stored till needed.

Furthermore, mixes C or D can be dissolved in solvents such as tetrahydrafurane then dried, after which the solid matter is roll-mixed and rolled into sheets. These sheets are cut into suitable sizes and stored till needed.

The ratio of ingredients contained in the conductive sheets can vary considerably however, a representative mix for polyvinylchloride tile is given the following table with ideal mixes E and F with the ratio of ingredients by weight.

The conductive sheet is prepared by heating and rollmixing ingredients as given in column E or F and rolling into sheets with a thickness of 0.2 to [0mm The sheets are then stored in rolls or cut into sheets of approximately LOOOmm. X 500mm. in size and kept in storage till needed.

The following is a detailed explanation of the manufacturing process depicted in FIG. 1 and FIG. 2 of con ductive floor tile shown in FIG. 3. The ingredients listed in column A are heated to l-l C. and rollmixed for about 1 minute in mixer l. The product 2 is then heated to l40l50C. and is further completely roll-mixed by rollers 3, 4. The mix adhering to roller 3 is cut by a cutter along a plane passing through the axis of the roller is then rolled up to form rolled body 5. This body is then heated to l0O-I40C. and is placed between marbling rolls 6, 7 and is further mixed and rolled on to roll 6 in the form of a rough sheet with a thickness of approximately lOmm. Hopper 9 is positioned over marbling rolls 6, 7 and contains colored slugs 10 which are produced from mix A and are 3mm. x 3mm. X 3mm. in size and ofa contrasting color to the base material, and conductive slugs 11 produced from mix C and are 5mm. X 5mm. X 5mm. in size, in the ratio of I13. The mixture of slugs l0 and I1 is imbedded into sheet 8 in a weight ratio of 20 percent during the time sheet 8 is rolled on to roller 6. Slugs l0 and I1 are heated and softened on entering sheet 8. Cutter 12 which has a length comparable to the length of roller 6 moves along a plane through the axis and cuts sheet 8 which can be removed from the roller. Sheet 13, composed of three such sheets stacked one upon the other. is placed on conveyor 14 and is fed into calender rolls 17. Top roller 15 is heated to approximately [00C. the lower roller 16 to approximately 80C. The

5 rough sheet is rolled into a sheet of basic tile I8. Sheet 18 is cooled by cooler 19 to a temperature of l4C. A cutter 20 moving perpendicular to the sheet surface and cutter bed 21 die-cuts the sheet into tiles 22 of approximately 300mm. X 300mm. square which are positioned on and transported by conveyor 23.

When composite sheet 13 is rolled in calender roll I7, coloring slugs l and conductive slugs I 1 contained therein are rolled and stretched to form numerous thin color flakes 24 and conductive flakes 25 in multiple layers. Numerous flowing streaks of colored flakes 26 and conductive flakes 27 appear on the top and bottom surface of tile 22. The numerous small conductive flakes 25 contained within the tile, and the numerous streaks of conductive flakes 27 on the top and bottom surface of tile 22 make contact or are pressed very close to each other.

Tile 22 is electrically conductive. As a result of meas urements, the volume resistivity is approximately 10' ohm-cm. and the maximum electrostatic charge was found to be less than l0 coulomb/cm? The coloring appearing on the surface of the tile is comprised of three colors namely the color of the tile body, color of the colored flowing streaks 26 produced by the colored flakes. and the black color of the conductive streaks 27. When the coloring slugs are not added the product will have only two colors.

The manufacturing process for producing the tile depicted in FIG. is explained by means of FIGS. 1 and 4. Similar to the aforedescribed process. the basic ingredients shown in A are heated and roll-mixed in mixer l, mixing roll 3, 4, marbling roll 6, 7. During this process conductive slugs 31 prepared from mix C and 2mm. X 2mm. X 4mm. in size are added in the weight proportion of percent and formed into rough sheet 28 with a thickness of mm. Conductive sheet 110 prepared from mix E is heated to about 100C. and is attached to the bottom surface of sheet 28. The resulting sheet 33 is placed on moving conveyor 34 and is fed into calender roll 37. With top roller 35 heated to about 100C. and bottom roller 36 heated to about 80C. the sheet is rolled to a thickness of 2mm to produce the basic tile material 38. Sheet 38 is cooled by Cooler 39 to about 40C. Cutter 40 and cutter bed 4l produce tiles 42 300mm. X 300mm. square which are moved by conveyor 43.

When stacked composite sheet 33 is rolled in calender roll 37 conductive slugs 3| which have been imbedded are softened by the heat and are rolled into flat layers and stretched to form numerous conductive flakes 45 in multiple layers. The conductive flakes appear on the surface of the tile in the form of streaks of flowing conductive flakes 47. Conductive sheet 110 applied to the back surface is rolled down to one-tenth ofits original thickness is partly torn or shredded and is introduced into the body of the tile as conductive flakes. Numerous conductive flakes 45 within the tile body. and flowing streaks of conductive flakes 47 appearing on the surface of the tile 42 and the conductive layer Ill formed on the bottom surface of the tile make contact with each other or are pressed into close proximity.

This tile 42 is electrically conductive. As a result of measurements volume resistivity is approximately 10 ohm-cm. and maximum electrostatic charge is less than 10"" coulomb/cm. The color of this tile consists ofthe color of the body and the black color of the conductive flakes 47 or a two color combination. Ifcolored slugs are added to the rough sheet 28 a three color combination can be obtained.

The process for manufacturing the tile depicted in FIG. 7 will be explained in detail by means of FIG. I and FIG. 6. Ingredients according to mix A are rollmixed in mixer I and mixing roll 3, 4, after which it is heated and further roll-mixed in marbling roll 6, 7. During the marbling process color slugs 50 prepared according to mix A and of size 2mm. X 2mm. X 4mm. in a contrasting color to the body color of the tile is imbedded in a weight ratio of4 percent. Conductive slugs 51 prepared according to mix C and of size 4mm. X 4mm. 5mm. are imbedded in a weight ratio of7 percent and a roughly rolled sheet 48 of l0mm. thickness is obtained. Conductive sheet 120 is applied to the top surface of sheet 48 and another sheet 48 of the same composition as 48 is placed on top to produce laminated sheet 53. This sheet 53 is placed on moving conveyor 54 and is fed into calender roll 57. The top roller 55 is heated to about I00C. and the bottom roller 56 is heated to about 80C. Laminated sheet 53 is rolled to a thickness of 2mm. to form the basic sheet material 58 for the tile. Sheet 58 is cooled to about 40C. by cooler 59. Cutter 60 and cutter bed 61 produce tile 62 of a size 300mm. X 300mm. Tile 62 is transported by conveyor 63.

When laminated sheet 53 is rolled in the calender roller 57 color slugs 50 and conductive slugs 51 which are embedded and softened by the heat, are rolled and stretched to form numerous flakes 64, 65 in multiple layers within the tile 62. Color and conductive flakes appear as numerous flowing streaks 66, 67 on the top and bottom surface of tile 62. Conductive sheet I20 is rolled to form conductive film layer 121, a part of which is torn apart. to form thin flakes 65 within the tile body. The numerous conductive flakes 65 in multiple layers, the thin conductive film layer I21, and the conductive flakes on the top and bottom surface 67 are electrically connected or are in extremely close proximity to each other.

The tile 62 described above is electrically conductive and has a volume resistivity of approximately 10 ohmcm. and the maximum eIectro-static charge is below l0 coulomblcm The color of the surface of this tile 62 is a combination of three colors. Furthermore. if the small color slugs 50 are not added to the rough rolled sheet 48 a two color combination will result.

The process for manufacturing the tile depicted in FIG. 10 is described in detail by means of FIG. 8 and FIG. 9. The basic ingredients as shown in A are mixed in mixer l, mixing roll 3, 4, and are heated and completely mixed in marbling roll 6. 7. During the marbling process, color slugs 70, prepared according to mix A and which are 2mm. X 2mm. X 4mm. in size, are added in the weight ratio of4 percent to produce rough sheet 68 with a thickness of 10mm. Conductive sheet 130 of about 2mm. in thickness and prepared according to mix E. is heated to about l00C. It is spread over the surface of rough sheet 68 after which another rough sheet 68' is placed over the conductive sheet 130 to form rough laminate sheet 73.

This sheet 73 is placed on moving conveyor 74 to calender roll 77, the top roller 75 of which is heated to approximately l00C. and the bottom roller 76 which is heated to approximately C, The rough sheet of 22mm. thickness is rolled into a sheet 78 of 2 mm. in

thickness. Sheet 78 is removed by conveyor 83. Sheets 78 are stacked to form sheet 93.

Laminate sheet 93 is placed on moving conveyor 94 and is fed into calender roll 97. The top roller 95 is heated to about 100C. and the bottom roller 96 is healed to about 80C. Sheet 93 of 8mm. thickness is reduced to 2mm. thickness by calender roll 97 to produce basic tile material 98 which is cooled by cooler 99 to about 40"Cv Cutter 100 and cutter bed cut the basic material to produce tile 102 of a size of 300mm. X 300mm. which is removed by conveyor [03.

When the rough laminate sheet 73; comprising sheets 68 and 68'. with conductive sheet 130 sandwiched therebetween is rolled by calender roll 77, the small color slugs 70, embedded in the base material, are softened by the heat and are rolled into numerous thin flakes contained within the tile body and appearing on the top and bottom surface in the form of thin flowing streaks. Conductive sheet I which forms layers within the body of the tile is rolled thin and torn apart in places to form numerous thin flakes within the body of the tile Sheet 93, which is formed by stacking four sheets 78, is rolled in calender roll 97, similar to calender roll 77. Small color flakes, conductive flakes and the conductivc sheet contained within 78 is further rolled and torn apart or shredded to form numerous small flakes within tile 102. i.e.. thin color flakes I04. conductive flakes I05 in multiple layers, streaks of color flakes 106 and conductive flakes 107 appear on top and bottom surface of the tile [02. The thin conductive flakes 105 contained within tilc 102 and thin conductive flakes forming streaks [07 on the top and bottom surfaces of the tile are electrically connected or are pressed into extremely close proximity.

This tile 102 is electrically conductive. actual measurements showing a volume resistivity of about l0 ohm-em. and maximum electrostatic charge of less than lt) "'coulomb/cm? This floor tile [02 has a three color combination. When the colored slugs 70 are not added to the roughly rolled sheet 68' a two color comhination results.

What we claim is: I. An electrically conducting floor tile, comprising:

an integral base sheet of non-conductive plastic material of a given color comprised of a plurality of self-adhered layers,

a plurality of individual slugs of plastic material embedded in each layer in a random pattern said slugs being of the same thickness as the layer in which they are embedded and of randomly elongated form,

a plurality of electrically conductive particles dispersed throughout each of the slugs including the opposite surfaces thereof forming conductive areas of flake-like appearance and of a different color than the base sheet,

at least some of the conductive areas being in electrical contact and the other of the conductive areas being in such close proximity to each other and to the at least some of the conductive areas as to form a grounding path for electrical charges between opposite surfaces of the tile.

2. An electrically conducting floor tile as defined in claim 1, wherein said tile has a volume resistivity of about l0 to 10'' ohm-cm. and a maximum electro static charge of less than I0" coulomb/cm".

3. A floor tile as defined in claim I further including a conductive sheet secured to one surface of the tile.

4. A floor tile as defined in claim 1, a second like floor tile coextensive therewith and a conductive sheet secured to and between the opposed surfaces of the tiles.

5. A floor tile as defined in claim 1 wherein the plastic sheet is polyvinyl chloride and the electrically conductive material of the conductive areas comprises carbon powder.

6. An electrically conductive floor tile according to claim I, wherein additional slugs of plastic material of a third color are embedded within each layer in a random pattern. 

1. An electrically conducting floor tile, comprising: an integral base sheet of non-conductive plastic material of a given color comprised of a plurality of self-adhered layers, a plurality of individual slugs of plastic material embedded in each layer in a random pattern, said slugs being of the same thickness as the layer in which they are embedded and of randomly elongated form, a plurality of electrically conductive particles dispersed throughout each of the slugs including the opposite surfaces thereof forming conductive areas of flake-like appearance and of a different color than the base sheet, at least some of the conductive areas being in electrical contact and the other of the conductive areas being in such close proximity to each other and to the at least some of the conductive areas as to form a grounding path for electrical charges between opposite surfaces of the tile.
 2. An electrically conducting floor tile as defined in claim 1, wherein said tile has a volume resistivity of about 1012 to 103 ohm-cm. and a maximum electrostatic charge of less than 10 12 coulomb/cm2.
 3. A floor tile as defined in claim 1 further including a conductive sheet secured to one surface of the tile.
 4. A floor tile as defined in claim 1, a second like floor tile coextensive therewith and a conductive sheet secured to and between the opposed surfaces of the tiles.
 5. A floor tile as defined in claim 1 wherein the plastic sheet is polyvinyl chloride and the electrically conductive material of the conductive areas comprises carbon powder.
 6. An electrically conductive floor tile according to claim 1, wherein additional slugs of plastic material of a third color are embedded within each layer in a random pattern. 